Purslane eyed as rich food source - US weed has beneficial nutrients

Agricultural Research, Dec, 1992 by Sean Adams

Hippocrates used it as a medicine. Henry David Thoreau found it in a cornfield, boiled it, and called it a "satisfactory dinner." Many Europeans today eat it as Thoreau did, or chop it up fresh and put it in their salads.

It's known as purslane--a plant that is a troublesome weed in many U.S. crops, especially vegetables. But recent research findings confirm that purslane is also a rich source of fatty acids, vitamin E, and other key nutrients--making it a prime candidate as a new vegetable crop.

There are about 200 species of purslane, the common name for a group of plants known as Portulaca. Scientists have focused on one annual species, P. oleracea, found around the world and in all 50 states. It is known for its persistence--it grows even in poor-quality soils with little water and resists disease. Its seeds have been found to survive for 40 years.

Researchers, including Helen A. Norman of the Agricultural Research Service in Beltsville, Maryland, have been conducting extensive studies of P. oleracea because of its high levels of omega-3 fatty acids. These nutrients, linked in some studies to reduced heart disease and other health benefits, are essential to building cell membranes, especially in the brain and eyes.

Humans and other mammals cannot make omega-3 fatty acids efficiently, so they must get them directly from food. Fish, a rich source of these fatty acids, obtain them by eating phytoplankton--minute, waterborne plants. Algae are high in essential dietary omega-3 fatty acids, while more advanced plants typically contain lower amounts.

But purslane is a major exception. Norman, at the agency's Weed Science Laboratory; James A. Duke at the ARS National Germplasm Resources Laboratory in Beltsville; Artemis P. Simopoulos of The Center for Genetics, Nutrition, and Health in Washington, D.C.; and scientist James E. Gillaspy of Austin, Texas, have confirmed that P. oleracea contains more of one omega-3 fatty acid---called alpha-linolenic acid--than any other green leafy vegetable yet studied.

Purslane can be eaten cooked or raw. In salads, it has a mild, nutty flavor and a crunchy texture much like bean sprouts. A 100-gram serving has about 300 to 400 milligrams of alpha-linolenic acid---10 times more than spinach, the researchers found.

Their findings were reported in the August 1992 issue of the Journal of the American College of Nutrition.

They've also discovered that purslane contains high levels of vitamin E---about 12.2 mg in a 100-gram serving. That's six times more than spinach. Vitamin E is an antioxidant that protects cell membranes from breaking down.

Other researchers have reported that purslane is the only higher plant to contain eicosapentaenoic acid, another omega-3 fatty acid, but Norman says she has not been able to confirm that.

ARS research at the U.S. Salinity Laboratory in Riverside, California, reported in 1989-90, shows that purslane would be a possible alternative crop in arid areas of the southwestern United States, because it is adaptable to both dry conditions and to salty soils often present where land is irrigated.-- By Sean Adams, ARS.

Helen A. Norman is at the USDA-ARS Weed Science Laboratory, Room 236, Bldg. 001, 10300 Baltimore Ave., Beltsville, MD 20705-2350. Phone (301) 504-6471, fax number (301) 504-6491.